The presently disclosed and/or claimed inventive concept(s) relates to a method for controlling the deposition of stickies in pulping and papermaking processes.
Problems associated with the formation of sticky deposits, comprising both inorganic and organic components, in pulping and papermaking processes are well known. “Pitch”, “stickies”, and “white-pitch” are commonly used terms for sticky hydrophobic materials produced during these processes, which adhere to surfaces and build up as aggregates in machinery.
In pulping processes using virgin fibres, “pitch” normally refers to natural resin hydrophobic materials, including fatty acids, esters and sterols, derived from the natural raw materials, most often wood. Pitch is especially prevalent in mechanical grades of pulp often used in recycled paper, where it is hydrolytically degraded and saponified to a lesser extent compared to the alkaline kraft process for making chemical pulp.
Paper can also be made from recycled fibres recovered from waste paper. In paper recycling both natural pitch and synthetic materials, such as polymers and binders used in paper, paper coating and printing inks, may form such tacky materials. In recycling industries these synthetic polymers are often referred to as “stickies” or “white pitch”.
For brevity, henceforth all of these sticky hydrophobic materials will be referred to collectively as “stickies”. Also for brevity, henceforth “papermaking” will be used to refer to both papermaking from virgin fibres and recycled fibres.
Stickies tend to form aggregates and adhere to surfaces in machinery, creating processing problems and degradation of the quality of the end product. Sticky deposits on surfaces, clogging of screens and filters hindering water passage and drainage, and deposits on cylinders and rolls are all frequently experienced and well known problems in this industry. Adhesion of stickies to surfaces reduces the effectiveness and efficiency of the manufacturing process, and results in interruptions and down-time for cleaning machinery, all of which have a negative economic impact. Adhesion of stickies to surfaces can also result in a reduction in product quality.
Various techniques have been published as possible methods for reducing the impact from sticky deposits. However, only few of these techniques have established themselves in common use in full scale manufacturing.
Mechanical devices, such as cyclones, are used in pulp and papermaking processes to separate materials of different gravity. US 2006124256(A1) describes the use of cyclones for the removal of high density stickies, followed by a flotation step. However, this method may require specific system modifications, for removing the currents of specific gravity. In many cases, long chain, hydrophobic organic materials have lower densities relative to the surrounding chemical environment. EP 0869218 describes adding a magnetic material having an affinity for the stickies with the subsequent removal of the aggregates in a magnetic field. However, this method also requires technical installations and a special design set up.
Chemical approaches for controlling stickies are also known, for example through the use of various types of organic polymeric materials having an affinity for stickies.
One of the most common approaches is to dose the system with a cationically charged material, due to the overall electronegative character of the stickies. Commonly used materials of this type are condensates of dicyandiamide with formaldehyde and poly-DADMAC. For example, EP1623067 describes the use of a crosslinked poly-DADMAC, while in EP1763609 an amphoteric polymer combined with anionically charged siliceous solid particles is used.
However, charged compounds have the potential to interfere with the chemistry of a papermaking system, and may have a negative impact on the finely tuned charge balance required for paper formation.
EP0569085 describes the use of a modified melamine formaldehyde polymer for this purpose, while EP1165677 describes using a polyphenolic compound modified with an amphoteric constituent. However, the use of bisphenols has toxicological issues. EP2044263 describes use of hydrophobically modified polyethyleneglycol.
In many cases, single polymers have been found to have limited performance, and combinations of polymers have been used instead. For example, EP0693147 and EP0693149 describe the use of native potato starch in combination with carboxyethylcellulose and/or methylhydroxypropylcellulose. EP1627107 describes the use of a cationic polymer combined with a hydrophobic modified hydroxyethyl cellulose, and EP0986670 describes using at least two materials selected from an oil-soluble or water-dispersible polymer, an oil-soluble or water-dispersible surfactant, a tackifier, and an oil-soluble or water-dispersible solvent. EP1425471 describes the use of a copolymer based on 75-95% acrylamide and 5-25% vinylacetate dosed to the pulp furnish. U.S. Pat. No. 5,510,439 describes a method for controlling pitch in papermaking systems through coagulation using a preferred reaction product of a major amount of diallyldimethylammonium chloride (95.0-99.9 parts) with a minor amount of vinyltrimethoxysilane (0.01-5.0 parts). In EP0825293 a combined dosage of a polyvinyl chloride, a cationic polymeric coagulant and a polymeric flocculent is used. CA2219139 describes the use of alkoxylation products (esters) of C10-C22 fatty acids and C10-C22 fatty acids containing an —OH group.
Pigments or adsorbents, such as bentonite, talc and clay having an affinity to stickies thus rendering them less tacky, are also commonly used materials for reducing their adsorption onto surfaces. For example, CN102733259 describes the use of talc, EP0989229 the use of a hydrophobic modified synthetic or natural mineral, U.S. Pat. No. 5,540,814 the use of cationic clay, and U.S. Pat. No. 5,080,759 the use of various organotitanium(IV) compounds. EP0740014 describes the use of siliceous particulate inorganic materials comprising at least one silicon-containing compound coated with a nitrogen-containing material containing one or more triazine rings. The particulate material is an aluminosilicate, such as kandite clay, coated with a homo- or copolymer comprising melamine formaldehyde-type structures. However, such minerals normally need high addition rates, and may lead to dusting of the final paper and/or increased sludge formation in waste water treatment plants because they can be very difficult to retain in the paper.
Stickies are hydrophobic, insoluble in water, and may develop increased tacky/adhesive properties under process conditions in pulp and papermaking. Other types of hydrophobic materials have thus been suggested for such treatment.
For example, WO9605361 describes the use of combinations of hydrocarbon-containing compounds, EP0517360 the use of a hydrocarbon solvent with a blend of surfactants, DE10324369 a fibre suspension cleaned for hydrophobic stickies by adding a triglyceride oil from various natural sources, EP0920551 the use of fatty alcohols for agglomerating stickies to such a size that they can be removed by screening, and EP1950342 a stickies control agent based on a PIT emulsion comprising a) dialkylamides as the main constituent and b) non-ionic surfactants for obtaining the emulsion. PIT refers to “Phase Inversion Temperature”, and requires the use of specifically combined surfactants for obtaining a phase inversion at a specific temperature, whereby small particles/droplets are formed. Fatty alcohol ethoxylates/partial glycerides or partial glycerides/alk(en)yl oligoglycosides or fatty acid amide alkoxylates/alk(en)yl oligoglycosides combinations are the preferred surfactants. However, a limitation of using non-ionic surfactants is that they do not prevent the formation of agglomerates of stickies, and their ability to disperse fine particles over a longer time is limited.
Organic surfactants have also been described for the reduction of stickies, often in combination with organic polymers. For example, CN101725064 describes a method of removing stickies through the use of combinations of non-ionic surfactants and anionic dispersing agents, such as (salts of) polyacrylamide, polyacrylic and polymetacrylic polymers. DE19929919 describes the use of non-ionic surfactants for dispersion in the high concentration phase, followed by flotation.
Proteins, including enzymes, have also been described for the reduction of stickies. For example, EP1268932 describes the use of whey proteins in combination with cationic compounds, and US2001020150 also describes the use of whey proteins. EP1802806 describes the use of various enzymes hydrolyzing or modifying the stickies in combination with anionic, non-ionic or cationic synthetic or natural adsorbents, such as silicates, carbonates or combinations thereof. DE102005034413 describes the use of an esterase enzyme (lipase) combined with a non-ionic, non-polymeric surfactant, and CN103074795 similarly describes the use of alkaline lipase for controlling stickies. EP1402109 describes the treatment of pulp from recycled paper with lipolytic enzymes to control stickies, the enzymes able to hydrolyze a polymer comprising vinylacetate monomer at neutral pH. CN101760976 applies an enzyme in combination with a soap deinking agent and a polyether surfactant. EP2092114 describes the use of enzymes in combination with non-ionic detackifiers in the form of hydrophobic modified hydroxyethylcellulose or a polyvinylacetate with a degree of hydrolysis from 50-100%. Proteins may have a pacifying effect on stickies, and enzymes can have a hydrolytic effect on specific chemical bonds. Enzymes are more or less specific in their action on types of chemical sites, and where esterases/lipases/lipolytic enzymes normally have a cleavage effect on ester bonds. However, the performance of enzymes is influenced by the physical/chemical environment, such as pH, temperatures and oxidizing materials. Aldehydes can for example bind to proteins and block the action of enzymes.
In addition to the methods previously cited, other techniques have been published using various types of chemical additives, either neat or in combination. For example, U.S. Pat. No. 5,009,746 describes the use of supercritical CO2 for controlling stickies, EP0698141 water glass in combination with fatty acid soaps and cationic flocculation/retention aids, and EP4923566 dissolved urea. EP1473405 describes how the surface of metallic drying cylinders and/or canvas coated cylinders may be treated by spraying with an amino- or epoxy-functional silicone oil, and related document EP2557226 describes coating drying cylinders in the paper machine (metallic or canvas coated) with an amino-modified polysiloxane.
Measuring the efficacy of the various techniques to control the deposition of stickies can to some extent be done under an artificial environment in the laboratory. However, the results obtained in the laboratory are often not reflected in full-scale industrial processing, where the stickies are influenced by the varying chemical and physical conditions throughout the process chain, where the process runs around the clock, more or less the whole year through.
There will thus always be physical and chemical interactions between the stickies present and the types of surfaces in the machinery where adhesion takes place. Thus, the type of furnish, the system design and processing parameters can each have an impact on the degree of deposition problems experienced. These variations may also limit the types of technology which can be used for combating problems caused by the deposition of stickies.
Only a few of the technologies described have become established as valuable methods for reducing stickies under full scale industrial operations. The industry thus still seeks a simple method for controlling the unwanted deposition of stickies in pulp and paper manufacturing systems, especially in relation to the paper recycling industry where problems from both natural and synthetic stickies occur. The materials used should be compatible with the existing process conditions, and should be able to remove and/or pacify stickies to such an extent that the process can run undisturbed for extended periods. The chosen method should not have a negative impact on the process, and should also be economical to use.
The presently disclosed and/or claimed inventive concept(s) seeks to address these issues with the prior art approaches.